The immunodeficiency inducing lentiviruses HIV-1 and SIV replicate in numerous tissues throughout the host, with early unchecked replication during the final stages of disease. The lung has been demonstrated in our previous studies to serve as a critical site of viral replication during the transition from clinical latency to AIDS in the SIV/macaque model of HIV-1 infection and disease induction in humans. This proposal outlines an experimental plan to comprehensively characterize the virologic and immunologic outcomes of infection in rhesus macaque lung tissues by SIV during the acute, clinically latent, and terminal stages of disease. Our hypothesis is that there are very specific virologic and immunologic events that occur in the lung immediately preceding the transition from clinical latency to AIDS, and we will seek to identify these events. For these in vivo analyses, cohorts of rhesus macaques will be inoculated intravenously with SlVdeltaB670 or biological and molecular clones derived therefrom, and in situ hybridization and immunohistochemical staining will be utilized to identify the numbers, locations, and types of productively infected cells in multiple parts of the lungs, in comparison to lymphoid tissues. In parallel, characterization of the composition of the lymphocytic and monocytic subsets will be performed. For these studies, lung tissue will be disaggregated and single cell suspensions generated to allow flow cytometric analyses of surface immunophenotype, in vitro killing analyses of SIV-specific cytotoxic T cell activities, and PCR/ heteroduplex mobility analyses of the T cell receptor Vbeta repertoire. In all experiments, investigations of lung tissues will be performed in comparison to bronchoalveolar lavage (BAL) cells, as the majority of existing data regarding the effects of HIV-1 on the immunologic environment in the lung are from BAL. These investigations will provide insight into the mechanisms by which primate lentiviruses alter the immunologic environment within the lung, leading to susceptibility to respiratory infections as well as systemic immunodeficiency.